In the art, there are numerous substances which are sensitive to light energy. The substances of interest generally fall into two classes. The first class comprises substances which undergo polymerization in response to applied light energy. The second class comprises light activated drugs which includes those drugs that produce a "singlet oxidation mechanism" in response to applied light energy. The second class of substances can be found in "photodynamic therapy" or "phototherapy" applications, while the first class of photo-sensitive substances are typically found in UV and visible light polymerization and photochemical curing of adhesives.
While there are known photochemical curing systems, these systems are designed as "bench-top" devices which tend to be bulky and therefore unsuitable for handheld applications. There are also known handheld devices. These devices also tend to be bulky and utilize quartz halogen light sources which produce considerable heat. Furthermore, the quart halogen light sources produce a broadband light output which has to be filtered to produce a selected spectral output. In many applications, for example, dental and medical, it is desirable to have a handheld or portable unit which produces a selected output and which can be easily manipulated in proximity to the patient.
The amount of light required depends on the application. For example, in a dental application, light dosage values in the range of up to 400 mW/cm.sup.2 are typically required. On the other hand, a medical application, such as photodynamic therapy of psoriasis and basal cells, requires a much lower dosage typically in the range of to 100 mW/cm.sup.2. Thus, it is desirable to have a portable device which can produce a range of light dosage output from low to high power values.
While known photochemical curing systems provide the capability to adjust the exposure time, they do not monitor the ongoing degradation of the intensity level produced by the light source. Thus, the performance of such a prior art system will steadily degrade over time unless the intensity level is manually measured and the exposure time adjusted accordingly. Therefore, it is also desirable to have the capability to monitor the intensity output for degradation in the light source.
Furthermore, in some applications, it may be desirable to increase the intensity level instead of the exposure time in order to provide an light energy output which is optimum for the curing application. Moreover, the light energy output level should be maintained at a consistent level over the operable life of the light source.